1. Field of the Invention
The present invention relates to a card-shaped or coin-shaped integrated circuit, hereinafter referred to simply as an IC, and more particularly to non-contact IC recording medium provided with a receiving coil and a transmission coil in which, when mounted in a reader/writer, these coils are magnetically connected with the corresponding coils of the reader/writer so that non-contact data transmission/reception paths are formed between the recording medium and the reader/writer.
2. Description of the Prior Art
In recent years, attention has been paid to an IC card incorporating an IC circuit such as a memory to store large capacity data. In order to store data in such an IC card or read the data from the IC card, the IC card is mounted in a reader/writer. Then, the electric contact on the IC card is brought into contact with that of the reader/writer so that the IC card is electrically connected with the reader/writer.
Meanwhile, the electric contact is attached to the IC card so that it is exposed externally. And also, usually such an IC card is always carried with a user so that dust is likely to be stuck to the electric contact or static electricity is likely to be generated there. If dust is stucked to the electric contact, the contact state between the respective electric contacts of the IC card and the reader/writer will become poor. If static electricity is generated at the electric contact of the IC card, a high voltage will be applied to the IC module within the IC card so that the IC module may be destroyed.
In order to obviate these problems, a means of connecting an IC card with a reader/writer through magnetic coupling has been proposed. This is referred to as a non-contact IC card. As disclosed in JP-A-61-226888, in this IC card, a card body is provided with coils for data transmission and data reception whereas a reader/writer is also provided with the corresponding coils for data transmission and data reception. When the non-contact IC card is mounted in the reader/writer, the corresponding coils are magnetically coupled with each other to form two-route data transfer paths having different directions.
In this way, the data transfer paths are formed in a non-contact manner through magnetic coupling so that the above problem attendant on an IC card provided with an electric contact does not arise.
Meanwhile, in order to drive the microcomputer incorporated in the non-contact IC card, a clock signal, hereinafter referred to simply as a clock is required. In a system of the IC card provided with an electric contact, the clock is supplied from the reader/writer to the IC card. Therefore, in the non-contact IC card, it can be proposed to supply the clock from the reader/writer. However, this requires undesired provision of a coil for clock transfer.
In order to obviate such difficulty, it has been proposed to provide a clock generating means within the non-contact IC card. However, this means has also the following defect. In order to stabilize the data transfer rate between the reader/writer and the non-contact IC card, usually, the reader/writer includes a quartz oscillator which is very stable as the clock signal generating means. Therefore, in order for the non-contact IC card to process the data transferred from the reader/writer at such a stable transfer rate and also transfer the processed data to the reader/writer, the clock generating means to be incorporated in the non-contact IC card must be a quartz oscillator which is stable and can generate the clock at the frequency which is exactly equal to that of the clock in the reader/writer. However, it is very difficult to locate the quartz oscillator, which inherently has a comparatively large size and thickness, within a limited inner space of the non-contact IC card.